1. Field of the Disclosure
The present disclosure is generally related to semiconductor devices and more particularly to signal-controlled oscillators.
2. Description of the Related Art
Radio communication devices, such as cellular telephones, usually include a voltage-controlled oscillator (VCO) as part of their circuitry. To produce the highest quality output signal, noise in the output signal of the VCO should be minimized. However, the reduction of current drain, for example, to extend battery life of a device, generally counteracts efforts to reduce noise at the output of a VCO. In addition, the desirable VCO qualities of guaranteed start-up and wide tuning bandwidth also create design trade-off problems with noise minimization. One method of reducing current drain is for the supply voltage to the VCO to be just large enough to support a specific application. However this practice can prevent the VCO from starting up properly when power is initially applied. A large supply voltage ensures that the oscillator will start in a predictable manner, while too small of a supply voltage may not provide enough energy to cause oscillation to begin. However, large supply voltages consume more power, which requires larger on-chip devices that increase parasitic capacitance and current drain, while reducing the Q and adversely affecting the tuned bandwidth of a system.
Another method of controlling output amplitude, and therefore current drain and noise, of a VCO is to provide a feedback signal that controls and limits the gain of the oscillator. This feedback signal however, is itself a source of additional noise and can require significant overhead to support applications with different output requirements. For example, a transmit VCO for GSM (Global System for Mobile Communications) technology would have a different operating requirement than that for WCDMA (Wideband Code Division Multiple Access).
Therefore, a system and/or method which limits these problems would be advantageous.
The use of the same reference symbols in different drawings indicates similar or identical items.